The present invention relates to radiation detectors and, more particularly, to a novel scintillator element having a trapezoidal cross-section for use in radiation detectors.
Many radiation inspection systems, such as X-ray systems of the computerized tomography type, require measurement of radiation flux with a high degree of precision. In a typical computerized tomography X-ray system, a degree of precision generally allowing less than 0.1% error is desirable. In medical X-ray technology, the time during which a patient is exposed to X-radiation is desirably as short as possible; a poly-energetic X-ray source is utilized to effect a shortened patient exposure time. In those radiation inspection systems, such as a computerized tomography system, a plurality of radiation detectors simultaneously measure the X-ray flux after differential absorption thereof upon passage through the patient, and the detector element of each detector must respond to X-ray signals in manner substantially identical to the response of all other detector elements, even though the X-ray signal received at any one particular detector of the plurality thereof has a variable X-ray spectrum and a widely varying intensity.
In radiation inspection systems utilizing solid state detectors, a scintillating element is utilized to convert the differentially absorbed radiation to optical photons, and means are provided for detecting the radiation-induced fluorescence from the scintillator. Typically, means are provided for collimating the incident radiation to limit the angle over which the radiation can enter the scintillator element. A typical X-ray detector for computerized tomography utilizes a collimating means consisting of flat plates of a high atomic number material such as tungsten or tantalum, arranged to be normally parallel to the direction of incidence of the X-ray flux, with a rectangular parallelopiped scintillator bar positioned between the plates and at least one photosensor arranged to intercept a major faction of the optical photons produced by the scintillator, without appreciably affecting the magnitude of the incident X-ray flux. The response of such a detector to X-ray energy is highly dependent upon not only the degree to which X-rays are scattered off the collimating plates, but also to the dimensional perfection of the rectangular parallelopiped scintillator element; typically, only a one-part-per-thousand deviation from a perfect rectangular parallelopiped shape can be tolerated. Accordingly, it is desirable to provide a radiation detector, of the scintillator element-collimator plate type, having a reduced response variation with change in scintillator element positioning.